fix: use X-Forwarded-Host first on app.proxy present (#1263)

lib/request.js

@@ -252,8 +252,10 @@ module.exports = {
   get host() {
     const proxy = this.app.proxy;
     let host = proxy && this.get('X-Forwarded-Host');
-    if (this.req.httpVersionMajor >= 2) host = this.get(':authority');
-    host = host || this.get('Host');
+    if (!host) {
+      if (this.req.httpVersionMajor >= 2) host = this.get(':authority');
+      if (!host) host = this.get('Host');
+    }
     if (!host) return '';
     return host.split(/\s*,\s*/)[0];
   },

test/request/host.js

@@ -53,22 +53,45 @@ describe('req.host', () => {
 
   describe('when X-Forwarded-Host is present', () => {
     describe('and proxy is not trusted', () => {
-      it('should be ignored', () => {
+      it('should be ignored on HTTP/1', () => {
         const req = request();
         req.header['x-forwarded-host'] = 'bar.com';
         req.header.host = 'foo.com';
         assert.equal(req.host, 'foo.com');
       });
+
+      it('should be ignored on HTTP/2', () => {
+        const req = request({
+          'httpVersionMajor': 2,
+          'httpVersion': '2.0'
+        });
+        req.header['x-forwarded-host'] = 'proxy.com:8080';
+        req.header[':authority'] = 'foo.com:3000';
+        req.header.host = 'bar.com:8000';
+        assert.equal(req.host, 'foo.com:3000');
+      });
     });
 
     describe('and proxy is trusted', () => {
-      it('should be used', () => {
+      it('should be used on HTTP/1', () => {
         const req = request();
         req.app.proxy = true;
         req.header['x-forwarded-host'] = 'bar.com, baz.com';
         req.header.host = 'foo.com';
         assert.equal(req.host, 'bar.com');
       });
+
+      it('should be used on HTTP/2', () => {
+        const req = request({
+          'httpVersionMajor': 2,
+          'httpVersion': '2.0'
+        });
+        req.app.proxy = true;
+        req.header['x-forwarded-host'] = 'proxy.com:8080';
+        req.header[':authority'] = 'foo.com:3000';
+        req.header.host = 'bar.com:8000';
+        assert.equal(req.host, 'proxy.com:8080');
+      });
     });
   });
 });